1. Field of the Invention
This invention relates to a magnetic material, and, more particularly, it is concerned with a low loss oxide magnetic material which is usable as a deflection yoke core for a high speed scanning cathode ray tube (hereinafter abbreviated as "CRT").
2. Discussion of Background
As the deflecting yoke core for CRT, there has long been used Mg-Mn-Zn series ferrite This material has been widely used both domestic and foreign as the standard ferrite material for the deflection yoke core, because it has high resistivity and hence vertical windings can be directly applied onto the core of such ferrite material with advantage.
On the other hand, owing to rapid diffusion in recent years of office automation (OA), computer-assisted-design (CAD), computer-assisted-manufacture (CAM), and so on, there is increasing demand for CRT for graphic display, monitor display, etc which are required to have high resolution. These CRT's are required to have high performance which is absent in the conventional CRT's for the household television sets, since such CRT's are scanned at high speed and therefore have high horizontal deflection frequency On account of this, with the core for the deflection yoke wherein the winding system for the horizontal and vertical windings, improvement in the convergence properties, etc. have been advanced energetically, the problems of the self-heat-generation of the core, and so on have become inegligible with increase in the horizontal deflection frequency, and the reduction in loss of the core is the urgent task.
The Mg-Mn-Zn series ferrite which is used at present as the standard material has been developed with a view to enabling the vertical windings to be directly wound on and around the core. However, while this ferrite material has less vortex loss which occupies in the total loss of the material because of its high resistance, the hysteresis loss thereof due to various influences such as composition of the material, crystal structure thereof, and various other factors is relatively great, the improvement of which has been the urgent task.
Therefore, when the core for the deflection yoke was manufactured with a low loss Mn-Zn series ferrite which is used as a main transformer material for the switching power source, etc., there could be observed that the temperature rise in the deflection yoke core was fairly improved due to reduction in the core loss. However, the ringing phenomenon took place on the screen of the CRT. Thus, it has become apparent that adoption of this CRT is not possible from the point of its image quality.
This ringing phenomenon, when taking the horizontal winding as an example, produces potential distribution between the adjacent layers of the windings, in case a voltage in the form of an impulse is introduced as an input, whereby capacity is generated between the adjacent scanning lines. Also, in general, when the frequency becomes higher, the floating capacity tends to increase. This can be inferred that there is brought about resonance between the component C of the capacity and the component L of the windings, and the deflection current is subject to the speed-modulation, with the result that there emerge on the screen the brightness-modulated vertical stripes.
On the other hand, in the vertical winding, there is brought about distributed capacity between the winding and the core at the result of applying the winding in the toroidal form directly on the core. On account of this, there is formed a distribution circuit consisting of distribution of the electrostatic capacity between the winding and the core, inductance of the winding, and resistance of the core. This circuit is symmetrical in its left and right sides If the horizontal winding is also symmetrical in its left and right sides, there should be no coupling of the horizontal winding with respect to the inductance of this circuit. If, however, there exists a certain asymmetry, there takes place coupling with the current flowing through the horizontal winding with the consequence that vibrating current flows locally in and through the vertical winding.
According to analyses done by the present inventor, it has been found that this vibrating current becomes increased, as the resistivity becomes smaller, and that the critical resistance is 10.sup.4 ohm-m. It goes without saying that the greater this value is, the more is it desirable.
From such standpoint, there has been proposed a low loss oxide magnetic material, while still retaining its high resistance. Such material is Ni-Cu-Mn-Zn series ferrite, which has attained its low loss which is approximately half that of the conventional Mg-Mn-Zn series ferrite and is utilized as the ferrite for the high speed scanning deflection yoke in a frequency range of from 64 KHz to 90 KHz.
However, the conventional low loss oxide magnetic material of the abovementioned composition contains therein nickel (Ni) which is expensive and is rare in the natural resources, on account of which there was a problem such that disadvantage in the aspect of its manufacturing cost could not be avoided.